From 9edc984239e058043c03117b7aa43e3ce8bfabd8 Mon Sep 17 00:00:00 2001
From: Phillip Cloud <417981+cpcloud@users.noreply.github.com>
Date: Wed, 25 Sep 2024 06:53:38 -0400
Subject: [PATCH] fix(clickhouse): fix truncating to date from a timestamp

---
 ibis/backends/clickhouse/tests/test_functions.py | 14 ++++++++------
 ibis/backends/sql/compilers/clickhouse.py        | 10 ++++++++--
 2 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/ibis/backends/clickhouse/tests/test_functions.py b/ibis/backends/clickhouse/tests/test_functions.py
index e4788026bc95e..2637860c4a745 100644
--- a/ibis/backends/clickhouse/tests/test_functions.py
+++ b/ibis/backends/clickhouse/tests/test_functions.py
@@ -495,14 +495,16 @@ def my_eq(a: int, b: int) -> bool: ...
 
 
 def test_timestamp_to_start_of_week(con):
-    expr = ibis.timestamp("2024-02-03 00:00:00")
-    expr1 = expr.truncate("W")
-    result = con.to_pyarrow(expr1)
-    assert result is not None
+    pytest.importorskip("pyarrow")
+
+    expr = ibis.timestamp("2024-02-03 00:00:00").truncate("W")
+    result = con.to_pyarrow(expr).as_py()
+    assert result == datetime(2024, 1, 29, 0, 0, 0)
 
 
 def test_date_to_start_of_day(con):
+    pytest.importorskip("pyarrow")
+
     expr = ibis.date("2024-02-03")
     expr1 = expr.truncate("D")
-    result = con.to_pyarrow(expr1)
-    assert result is not None
+    assert con.to_pyarrow(expr1) == con.to_pyarrow(expr)
diff --git a/ibis/backends/sql/compilers/clickhouse.py b/ibis/backends/sql/compilers/clickhouse.py
index 46201bfff8f49..d80917df0d39d 100644
--- a/ibis/backends/sql/compilers/clickhouse.py
+++ b/ibis/backends/sql/compilers/clickhouse.py
@@ -383,15 +383,21 @@ def visit_TimestampTruncate(self, op, *, arg, unit):
 
         if short in ("s", "ms", "us", "ns"):
             arg = self.f.toDateTime64(arg, op.arg.dtype.scale or 0)
-        return self.f[func](arg)
+        return self.cast(self.f[func](arg), op.dtype)
 
     visit_TimeTruncate = visit_TimestampTruncate
 
     def visit_DateTruncate(self, op, *, arg, unit):
-        if unit.short == "W":
+        if unit.short == "D":
+            # no op because truncating a date to a date has no effect
+            return arg
+        elif unit.short == "W":
             func = "toMonday"
         else:
             func = f"toStartOf{unit.singular.capitalize()}"
+
+        # no cast needed here because all of the allow units here return `Date`
+        # values
         return self.f[func](arg)
 
     def visit_TimestampBucket(self, op, *, arg, interval, offset):